Math = Love: New Puzzle: Only 'Takes' and 'Adds'

Tuesday, September 15, 2020

New Puzzle: Only 'Takes' and 'Adds'

I did a lot of thinking this summer about how I wanted to incorporate puzzles into my classroom this year. Over the last few years, puzzles are one of the things I've become known for sharing on my blog. Hello, I have an entire page on my blog dedicated to all things puzzles.


There are so many excellent puzzles out there in the world, but my favorites for the classroom are those that involve pieces to manipulate. I love putting magnets on the back of each piece and hanging the puzzle up on my dry erase board for students to play with throughout the week.


We've been teaching face-to-face since school started back in late August with required social distancing and no shared supplies/materials. This means I have to rethink my weekly puzzle station since it often involves an entire group of students congregated at the dry erase board while manipulating the same set of puzzle pieces.

Someone on twitter suggested mini laminated versions of each puzzle that get sprayed with lysol between uses. But, I'm at the point this year where I feel like I already have too much on my plate and something like sanitizing puzzle pieces on a daily basis might just send me past my tipping point.

So, I'm currently on a quest to build myself a new collection of puzzles to post in my classroom that students can solve that don't involve any pieces to touch and manipulate.


Since I have many students this year who I also taught last year, I went ahead and made a no touching sign to hang under my puzzle of the week sign. A blog commenter suggested awhile back that I try matte finish Krylon spray to keep my laminated stuff from having an annoying glare. I finally tried it out, and I am super impressed with the results. 

Check out the difference between the no touching sign I sprayed and the puzzle of the week sign I didn't. 



This week, we'll be testing out the concept of no touching puzzles with Brian Bolt's Only 'Takes' and 'Adds' puzzle from Mathematical Cavalcade (affiliate link).


I reworded the task a bit to make it easier to turn into a poster. Write down the digits 9 to 1 in descending order. Make 100 by adding only addition and subtraction signs.

For example: 98 - 7 + 6 + 5 + 4 - 3 - 2 - 1 = 100.

How many ways can you find? Can you make 100 using only 4 signs?
I love this task for several reasons. First, I appreciate the fact that there are multiple solutions. When I solved the problem myself, I found it pretty easy to find A solution. It was much more difficult to find a solution using only 4 signs. There was a nice bit of logical thinking that I had to go through to figure out how to organize my work to make finding a solution more feasible. I also really appreciate that the task provides one solution as an example. This prevents having to specify, for example, that concatenation is allowed.

Want to print a copy of the puzzle for your own classroom? I've uploaded the file here.

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